My personal feeling is that "If it ain't broke... keep it working"
You may want to update to the latest firmware; and servicing might be a good idea if the camera or lens has gotten really dusty. But with a minimum of moving parts, if the camera works great keep going with it. It's not as though you need to have the belts tightened...

Never serviced any of my EX's other than a good clean with a paint brush to get dust and dirt out of all the little corners etc. Also as suggested above I always used to check the FB every month or so.